`loadView()` override needed if no interface builder

[gaborcsardi]

Thanks for the great project! Just wanted to mention that AFAICT if you are not using interface builder, then you need to write loadView() manually in the controllers, otherwise you get a crash:

  override func loadView() {
    self.view = NSView()
  }

If this is correct, then maybe it is worth mentioning in the README.

[sindresorhus]

I don't think this is the place to document how view controllers work.